1. Field of the Invention
This invention relates generally to plasma reaction devices, and more particularly to such devices used for plasma etching, plasma deposition, and plasma refining, etc. and make use of cylindrical, concentric electrodes.
2. Description of the Prior Art
Plasma reaction techniques are widely used in the manufacture of semiconductor devices. These techniques are used, for example, in etching, deposition and refining semiconductor wafers. Plasma reaction devices of the type using a cylindrical reaction chamber about which an exterior electrode is disposed and a cylindrical interior electrode with plasma-diffusion through-holes are known. These devices have the plasma-diffusion through-holes distributed uniformly throughout the interior electrode and are of a uniform cross section and each of a same cross section area dimension.
These devices have the reaction chamber connected to a vacuum pump and a working gas is let into the reaction chamber through a base having inlet openings. A stage is mounted in the interior of the reaction chamber for holding a workpiece interiorly of the interior electrode for treatment of an exposed surface of the workpiece with a plasma of the working gas. The plasma is developed by exciting the working gas with a high frequency voltage applied across the electrodes from a high frequency voltage source.
These known plasma reaction devices, however, do not develop a uniform plasma concentration over the surface of a workpiece being treated. This arises from the lack of accurate control of uniformity of the plasma, in the reaction chamber, by the plasma-diffusion mechanism of the through-holes or openings in the interior electrode.
As a consequence of the lack of uniformity of plasma diffusion there is lack of uniformity of reaction rates for example, lack of uniformity of treatment on the surface such as lack of uniform etching rates thereof.